Porta Asinaria:
a gate in the Aurelian wall on the Caelian, just south-west of the Porta S. Giovanni (Ill. 42), through which the
Via Asinaria(q.v.)
passed (DMH; Procop. BG I.14.14; III.20.15). This road was of no importance, and the massiveness of the gate may be due to the vicinity of the Lateran palace. The name is given correctly by Magister Gregorius (JRS 1919, 19, 46); by other writers of the Middle Ages it was called Porta Asinaria Lateranensis (Mirab. 4) and Porta S. Johannis (GMU 88; RII.406, who distorts the ancient name into Assenarica). It was closed in 1408, but probably opened again, and not permanently closed until the modern Porta S. Giovanni was built in 1574.

The existing structure of brick-faced concrete is not later than Honorius. It shows traces of several changes of plan or additions in the same material, and is one of the best preserved of all the gates. It has two long bastions with semicircular fronts and three rows of windows, and these bastions are flanked by square staircase towers: and above the archway is the usual long chamber in the masonry with two rows of windows, of which the lower interrupts an earlier embattled breastwork (Jord. I.1.363; REII.1581; PBSRIV.42‑43; Reber 535‑536; TII.28‑31; XI.20‑27; BC 1917, 194; 1927, 64; Discovery cit.). For a relief which may represent it, see Lauer, Le Latran, p19, fig. 7.

Images with borders lead to more information.
The thicker the border, the more information.
(Details here.)

The Dictionary's table of bibliographical abbreviations is
here;
it includes links to those complete works that are online.